Belt squealing all the time in a 94 Geo Prizm

Recently my husband changed the belt in my 1994 Geo Prizm because the old belt was worn and badly in need of replacement. Now every time I start the car and drive it, it screeches loudly. Sometimes if I turn on the AC, the screeching will stop for a bit but the car begins to chug and run roughly (it's a manual). He has tried to tighten the belts (AC and serpentine)but nothing seems to help. This is terribly annoying and distracting to drive while my car screams like a banshee. Help me please!